Обсуждение: transactions and ecpg

I'm looking at some code that a coworker ported from Informix to
Postgres 9.0. The Informix database did not have transaction logging
enabled thus no begins/aborts/commits/rollbacks where in the original
code. The way the code has been ported there are still no begin
statements in the code, only commit and rollback after data changing
statements are executed.

Question 1: After a commit/rollback does the next SQL statement
implicitly begin a transaction?

Question 2: If we're just examining data via SELECT statements should we
be issuing COMMIT statements after or are they only required for data
modifying operations?

Thanks in advance,
Wayne